<!DOCTYPE html>
<html xmlns:th="http://www.thymeleaf.org">
<head>
  <meta charset="UTF-8">
  <title>Title</title>
</head>
<body>
<form action="/student/update">
  <input type="hidden" name="id" th:value="${stu.id}">
  姓名：<span th:text="${stu.name}"></span><br>
  生日：<span th:text="${stu.birthday}"></span><br>
  电话：<input type="text" name="phone" th:value="${stu.phone}"><br>
  <input type="submit" value="修改">
</form>
</body>
</html>